The present invention relates to diagnosing errors in data processing systems and, more particularly, to diagnostic circuitry for use in diagnosing errors in the processor of a data processing system.
There have been proposed in the past a number of approaches for use in diagnosing operational errors in the processor of a data processing system. For example, in U.S. Pat. No. 4,253,183, issued to Allen G. Taylor et al., there is provided circuitry for recording signals or test data at various test points in a processor in response to a snapshot command. The signals or test data are used, for example, by a field engineer in order to analyze the operation of the processor.
Other approaches have been proposed in the past for recording data generated during the operation of the processor, such data being generated in response to a diagnostic command or being generated during the performance of actual tasks by the processor. Furthermore, it has been known in the past to provide diagnostic circuitry for stopping the operation of a processor at the occurrence of a specified command, as illustrated in U.S. Pat. No. 4,048,671, issued to Robert W. Callahan, et al.
While the incorporation of diagnostic circuitry in a processor to aid in later diagnosis by a field engineer has been known, such diagnostic circuitry often increases the cost of manufacturing the processor. Furthermore, a number of different diagnostic operations may be desirable when a field engineer services a processor, and to incorporate circuitry for accomplishing each of these diagnostic operations often consumes processor components and space which might be better used by the processor to carry out normal processor functions or operations.
There has, accordingly, arisen a need for diagnostic circuitry for use with a data processor that is relatively simple and inexpensive, but that can be used by a field engineer to carry out a number of important diagnostic operations.